The invention relates to a method of electrochemically machining a workpiece by means of an electrode, said method comprising the steps of:
setting a gap between the electrode and the workpiece, which gap is filled with an electrolyte, PA1 feeding an electric current through the electrolyte in the gap via the electrode and the workpiece in order to machine the workpiece, PA1 generating a measurement signal comprising information about possible sparks in the gap, and PA1 protecting the electrode and/or the workpiece against damage by reducing the current when a parameter of the measurement signal exceeds a certain threshold value. PA1 an actuator for setting a gap between the electrode and the workpiece, PA1 fluid transport means for flushing the gap with an electrolyte, PA1 power supply means for feeding an electric current through the electrolyte in the gap via the electrode and the workpiece in order to machine the workpiece, and damage prevention means comprising PA1 measurement means for generating a measurement signal comprising information about premonitory phenomena of partial spark discharges in an inter-electrode gap, PA1 detection means for generating a stop signal when a parameter of the measurement signal exceeds a threshold value, and PA1 reduction means for reducing said current upon detection of said stop signal.
The invention further relates to an apparatus for electrochemically machining a workpiece by means of an electrode, said apparatus comprising:
measurement means for generating a measurement signal comprising information about partial discharge precursors of spark discharges in the gap, PA2 detection means for generating a stop signal when a parameter of the measurement signal exceeds a threshold value, and PA2 reduction means for reducing said current upon detection of said stop signal.
The invention also relates to a damage prevention means comprising
Such a method, apparatus and damage prevention means are known from GB 2 140 824. The known method is applied in an apparatus for electrochemically machining (ECM) a workpiece with an electrode. According to this method a gap is set between the electrode and the workpiece. This gap is filled with an electrolyte and a current from a power supply is fed through the electrolyte via the electrode and the workpiece. In order to prevent the generation of an electric arc across the gap, individual spark discharges are detected by means of an electric circuit connected to the electrode and the workpiece. The electric circuit comprises filter means to distinguish noise caused by spark discharges from noise generated by the power supply. Upon detection of spark discharges the power supply is disabled and damage due to an electric arc is prevented. A disadvantage of the known method, apparatus and damage prevention means is that the spark discharges themselves also damage the electrode and the workpiece. Especially when the inter-electrode gap is smaller than 50 micrometers, spark discharges should be prevented because the resulting damage may require replacement of the electrode.